Parler, the social network popular with Trump supporters said on Thursday that it had been working with law enforcement for months to identify possible illegal activity, including notifying authorities of specific threats to the Capitol ahead of the Jan. 6 assault on Congress.
Parler said in a letter to Representative Carolyn B. Maloney, Democrat of New York and chair of the House Oversight Committee, that it formalized its relationship with the F.B.I. in November “to facilitate proactive cooperation and referrals of violent threats and incitement to law enforcement.”
The company said that it sent the bureau dozens of concerning posts written by its users, including some related to the deadly Jan. 6 attack.
“In the days and weeks leading up to Jan. 6, Parler referred violent content from its platform to the F.B.I. for investigation over 50 times,” the company said in its letter. “Parler even alerted law enforcement to specific threats of violence being planned at the Capitol.”
The letter raises fresh questions about whether the F.B.I. took seriously enough threats of violence made ahead of Jan. 6, when Congress formally certified the Electoral College after President Donald J. Trump had spent weeks spreading baseless claims about election irregularities.
The F.B.I. declined to comment on the letter or on what it has done with any information it has received from Parler.
Four days before the riot, the company said it gave the F.B.I. posts made by a user who said that he would attend the Jan 6 rally in body armor because “it’s no longer a protest.”
“This is the final stand where we are drawing the red line at Capitol Hill,” according to quotes from his messages that Parler shared with Congress.
“This is not a party until they announce #Trump2020 a winner,” the user wrote. “Don’t be surprised if we take the #capital [sic] building.”
In late December, the company said that it gave the F.B.I. three screenshots of particularly violent rhetoric from a user who threatened to kill politicians and who specifically threatened former Attorney General William P. Barr. And on Christmas Eve, it gave the F.B.I. a post by a user who said that he was looking for “some guys that are planning on lighting up Antifa” when they came to Washington on Jan. 6 because he wanted to “start eliminating people”
“Even after the violent attacks stopped, Parler continued to dutifully and proactively report posts to the F.B.I. where users threatened additional violence,” the company said in its letter.
Parler was embraced by conservatives after the November election, as Twitter and Facebook cracked down on misinformation around the election and kicked Mr. Trump off their platforms for incendiary speech.
The social network became a conservative cause célèbre in January, when mainstream companies like Apple, Amazon and Google removed it from their app stores and refused to provide it with technical services, claiming that it had allowed too much content that encouraged violence and crime.
The company came back on line last month with the help of a network of small web-hosting firms.
Separately on Thursday, top Democrats sent letters to the White House, the Justice Department, the F.B.I., the Pentagon, Mayor Muriel Bowser of Washington, the Park Police, the Metropolitan Police and some cabinet officials requesting all documents and communications related to the attack on the Capitol and its aftermath. The letters were signed by the chairs of the House committees on oversight, judiciary, intelligence, homeland security, administration, armed services and appropriations.